Method for making diarylhalonium salts

ABSTRACT

A method is provided for making certain diaryliodonium salt photoinitiators, based on the initial formation of a diaryliodonium bisulfate. Methylene chloride is substituted for acetic acid during the reaction between potassium iodate and benzene in the presence of acetic anhydride and sulfuric acid. The diaryliodonium bisulfate is then reacted with a counterion source, such as a metal salt, to produce the desired diaryliodonium salt which can be used as a photoinitiator. The iodonium salt photoinitiators made by the method of the present invention can be used to make UV curable compositions.

The present invention is directed to a method for making diaryliodoniumsalt photoinitiators. More particularly, the present invention relatesto the use of methylene chloride as a solvent in place of acetic acid informing a diaryliodonium bisulfate reaction intermediate.

Prior to the present invention, as shown by Crivello U.S. Pat. No.3,981,897, assigned to the same assignee as the present invention,certain halonium salt photoinitiators, such as diaryliodoniumhexafluoroarsenates, were prepared by initially forming a diaryliodoniumbisulfate of the formula,

    [(R).sub.a (R.sup.1).sub.b I].sup.+ [HSO.sub.4 ].sup.-     ( 1)

followed by reacting the diaryliodonium bisulfate with a hexafluorocompound, such as potassium hexafluoroarsenate, where R is a monovalentaromatic organic radical, R¹ is a divalent aromatic organic radical, ais a whole number equal to 0 or 2, b is a whole number equal to 0 or 1,and the sum of a+b is equal to 1 or 2, or the valence of I.

The above described method of Crivello patent 3,981,897 can be used toproduce a variety of diarylhlaonium hexafluoro salt photoinitiators, butthe procedure can involve 16 hours or more of reaction time. Inaddition, product yields are often difficult to predict because theresults are frequently not reproducible. As shown by Crivello, aprincipal step in the preparation of the photoinitiator is based on theprior formation of the intermediate diarylhalonium bisulfate salt offormula (1). A method for making these diaryliodonium bisulfate saltsshown by D. A. Berry et al, Twelfth International Congress, Pure andApplied Chemistry, New York, N.Y., September 1951, page 465. The Berryet al method involves the direct coupling of benzene with iodyl sulfatewhich can be generated by potassium iodate in the presence of a mixtureof acetic acid, acetic anhydride and sulfuric acid. The Berry et almethod, based on the use of acetic acid-acetic anhydride and sulfuricacid has been found to require long reaction times and often results inlow yields and is difficult to reproduce.

The present invention is based on the discovery that a significantimprovement in reproducibility and reduced reaction time as well ashigher yields can be achieved with the procedure for makingdiaryliodonium bisulfate salts of formula (1), hereinafter referred toas the "bisulfate salts", if the acetic acid used in the reactionmixture is replaced with methylene chloride. The improved resultsachieved with the use of methylene chloride in place of acetic acid inthe synthesis of the bisulfate salts can be achieved if the reaction isrun at a temperature of from about -25° C. to +25° C., and preferably-5° C. to +5° C.

There is provided by the present invention, a method for making thebisulfate salts of formula (1) which comprises

(A) effecting a coupling reaction at a temperature of from -25° C. to+25° C. between a C.sub.(6-30) aromatic compound and potassium iodate inthe presence of a mixture consisting essentially of methylene chloride,acetic anhydride and sulfuric acid, and

(B) recovering the diaryliodonium bisulfate salt from the mixture of(A).

The bisulfate salt can be reacted with a metal salt of the formula,

    MQ,                                                        (2)

to produce by a metathesis, a diaryliodonium salt of the formula,

    [(R).sub.a (R.sup.1).sub.b X].sup.+ [Q].sup.-              ( 3)

where R, R¹, X, a and b are as previously defined and Q is an anion,such as a halogen ion, for example, chloride, bromide, fluoride, iodide,etc., YF₆, where Y is selected from a Group Va element such as P, As andSb, NO₃ ⁻, C1O₄ ⁻, CF₃ SO₃, PO₄ ⁻³, SO₄ ⁼, HSO₄ ⁻, CH₃ C₆ H₅ SO₃ ⁻, etc.The diaryliodonium salts of formula (3) can be used as photoinitiatorsas shown by the above Crivello U.S. Pat. No. 3,871,897, Smith U.S. Pat.Nos. 3,729,313, 3,808,006, etc.

Radicals included by R can be the same or different aromatic carbocyclicor heterocyclic radicals having from 6-20 carbon atoms, which can besubstituted with from 1-5 monovalent radicals selected from C.sub.(1-8)alkoxy, C.sub.(1-8) alkyl, nitro, chloro, etc., R is more particularly,phenyl, chlorophenyl, nitrophenyl, methoxyphenyl, pyridyl, etc. Radicalsincluded by R¹ are divalent radicals, such as ##STR1##

Some of the bisulfate salts of formula (1) are, for example,diphenyliodonium bisulfate, 4,4'-dichlorodiphenyliodonium bisulfate,4,4'-dibromodiphenyliodonium bisulfate, 3,3-dinitrodiphenyliodoniumbisulfate, 4,4'-dimethyldiphenyliodonium bisulfate,4,4'-bissuccinimidodiphenyliodonium bisulfate,3,3'-dinitrodiphenyliodonium bisulfate, 4,4'-dimethoxydiphenyliodoniumbisulfate.

Included by the Group Va metal hexafluoride salts of formula (2) are,for example, NaPF₆, NaAsF₆, KSbF₆, KAsF₆, Ca(PF₆)₂, Mg(AsF₆)₂,HPF₆,HAsF₆, HSbF₆, Ba(AsF₆)₂, Pb(PF₆)₂, Zn(AsF₆)₂, etc.

Included by the diaryliodonium salts of formula (3) are, for example,compounds such as ##STR2##

In the practice of the invention, the iodonium bisulfate salt isinitially formed by agitating a mixture of aromatic compound, potassiumiodate, methylene chloride, sulfuric acid and acetic anhydride. Suitablearomatic compounds include, for example, benzene, toluene, o-xylene,m-xylene, p-xylene, chlorobenzene, bromobenzene, alkylbenzene,nitrobenzene, N-phenylmaleimide.

It has been found that substantially two moles of the aromatic compoundto one mole of potassium iodate will provide for effective results.However, a proportion of from 6 moles to 2 moles of aromatic compoundper mole of potassium iodate can be used. Sulfuric acid, methylenechloride and acetic anhydride can be employed in excess amounts, whilethe sulfuric acid is preferably utilized at from 1 mole to 3 moles ofsulfuric acid per mole of potassium iodate. The solids concentration ofthe mixture can vary from 10% to 50% by weight.

After the bisulfate salt has been formed, it can be recovered from themixture. Alternatively, water can be added to the mixture to dissolvethe potassium bisulfate without separating the bisulfate salt. Anaqueous solution of the metal salt of formula (2) can then be addeddirectly to the mixture with stirring, resulting in the formation of thediaryliodonium metal salt. The diaryliodonium metal salt can berecovered as a precipitate from the mixture and thereafter filtered,washed and dried by standard techniques.

In order that those skilled in the art will be better able to practicethe invention, the following examples are given by way of illustrationand not by way of limitation. All parts are by weight.

EXAMPLE 1.

There was added 25 parts of concentrated sulfuric acid in a dropwisemanner to a mixture of 25 parts of potassium iodate, about 32 parts ofbenzene, about 50 parts of acetic anhydride and about 115 parts ofmethylene chloride. The mixture was maintained at a temperature of 0°-5°C. for 1.5 hours and then stirred at room temperature for 4 hours. Fiftyparts of distilled water was then added to the mixture to dissolvepotassium bisulfate, followed by the addition of 27 parts of potassiumhexafluoroarsenate dissolved in 100 parts of water. The mixture was thenstirred for 2 hours resulting in the precipitation of a product. Theproduct was filtered and washed with hexane. The salt was then dried at50° C. in vacuo. There was obtained 34.6 parts or a 63.5% yield ofproduct. Based on method of preparation, the product wasdiphenyliodonium hexafluoroarsenate.

A 3% mixture of the above hexafluoroarsenate salt in 4-vinylcyclohexaneoxide is irradiated for 0.5 minutes under a G.E. H3T7 mercury arcultraviolet lamp. There is obtained a cured tack-free film.

The above procedure is repeated, except that in place of the methylenechloride, there is used 115 parts of acetic acid. In addition, thesulfuric acid is added to the mixture dissolved in acetic anhydride. Themixture was stirred at around 5° C. for 4 hours. The mixture was thenfiltered. There was added 2000 parts of distilled water to the filtrate,followed by 200 parts of diethylether. The aqueous layer was thenseparated and extracted with diethylether. There was then added to theaqueous solution, 26 parts of potassium hexafluoroarsenate. The mixturewas stirred for 2 hours. A white precipitate was obtained which wasfiltered and washed with water and dried in vacuo. There was obtained 24parts of diphenyliodonium hexafluoroarsenate representing a 30% yield.

The above procedure employing acetic acid was repeated, except that thereaction mixture was stirred at around 5° C. for 18 hours, instead of 4hours. There was obtained about a 63% yield of the diphenyliodoniumhexafluoroarsenate.

The above results show that the method of the present invention providesa more rapid procedure for making diarylhalonium hexafluoro salts asshown by formula (3). The method of the present invention provided ayield of about 63% after a reaction period of about 6 hours. However,when the same reaction was repeated, except that the acetic acid wassubstituted for methylene chloride, the yield was reduced to 30%. Itrequired a total reaction time of about 18 hours to obtain a yield whichwas comparable to that provided by the method of the present inventionwhich was achieved in approximately one-third of the time.

EXAMPLE 2

There were added 45.5 parts of concentrated sulfuric acid to a stirredmixture at 0° C. consisting of 25 parts of potassium iodate, 35 parts oftoluene, 149 parts of methylene chloride and 54 parts of aceticanhydride. Addition of the sulfuric acid required 0.5 hours. Thereaction was allowed to proceed at 0° C. for four hours. After thisperiod, 50 parts of water were added to dissolve the potassium bisulfatefollowed by the addition of 27 parts of potassium hexafluoroarsenate in100 parts of water. This two-phase mixture was allowed to stir for 2hours. The methylene chloride layer was removed and diluted with 133parts hexane resulting in the precipitation of 24.8 parts representing a43% yield of 4,4'-dimethyldiphenyliodonium hexafluoroarsenate. Thestructure of the compound was identified on the basis of its meltingpoint, 166°-167° C., and by its ultraviolet and nuclear magneticresonance spectrum.

EXAMPLE 3

Following the procedure of Example 1, 25 parts of potassium iodate, 45parts of N-phenylmaleimide, 160 parts of methylene chloride and 54 partsof acetic anhydride were combined. To this reaction mixture there wereadded slowly with vigorous stirring, 45 parts of concentrated sulfuricacid over the course of 0.5 hours while maintaining the temperaturebelow 5° C. The reaction mixture was held at this temperature for 4hours. Fifty parts of water were then added to dissolve the potassiumbisulfate. On addition of the water, rapid precipitation of a yellowproduct occurred which was filtered and washed with ether. The product,obtained in a 72% yield, was determined on the basis of its nuclearmagnetic resonance spectrum and its analysis to be4,4'-bis-N-phenylmaleimidoiodonium bisulfate, ##STR3##

A solution of 10 parts of ammonium chloride in 20 parts of water wasadded to an aqueous solution of 20 parts of the above iodoniumbisulfate. An immediate precipitate of4,4'-bis-N-phenylmaleimidoiodonium chloride was obtained.

EXAMPLE 4

A mixture of 25 parts of potassium iodate, 39 parts of t-butyl benzene,54 parts of acetic anhydride and 153 parts of methylene chloride wasstirred and cooled to 0° C. There were added slowly, 46 parts ofconcentrated sulfuric acid to maintain the reaction temperature below 0°C. After completing the addition, the reaction temperature wasmaintained at 0° C. for 1-1.5 hours and then allowed to stir at roomtemperature for 3.5 hours. The total reaction time was 4-5 hours. Fiftyparts of distilled water was added to dissolve the potassium bisulfate.There was then added 21.5 parts of potassium hexafluorophosphate. Afterstirring for 15 minutes, the methylene chloride solution is separatedfrom the mixture and the product is triturated with ethylether. The saltis filtered and dried in vacuo to give 33.2 parts or a 52.7% yield ofdi(p-t-butylphenyl)iodonium hexafluorophosphate.

EXAMPLE 5

A mixture of 25 parts of potassium iodate, 40 parts of o-xylene, 54parts of acetic anhydride, and 153 parts of methylene chloride wasstirred and cooled to 0° C. There were slowly added 46 parts ofconcentrated sulfuric acid to maintain the reaction tmeperature below 0°C. After completing the addition, the reaction was maintained at 0° C.for 1-1.5 hours. The mixture was stirred at room temperature for anadditional 3.5 hours. The total reaction time was 4-5 hours. Then 50parts of distilled water was added to dissolve the potassium bisulfate.There was then added 21.5 parts of potassium hexafluorophosphate inabout 250 parts of water. After stirring 15 minutes, the methylenechloride layer is separated and the product is triturated withethylether. The salt is filtered and dried in vacuo to give 27.9 partsor a 49.2% yield of di(3,4-dimethylphenyl)iodonium hexafluorophosphate.

Although the above examples are limited to only a few of the very manyvariables useful in the practice of the method of the present invention,it should be understood that the present invention is directed to thepreparation of a much broader class of diaryliodonium saltphotoinitiators as shown in the description preceding these examples.

What we claim as new and desire to secure by Letters Patent of the U.S.is:
 1. In a method for making bisulfate salts of the formula,

    [(R).sub.a (R.sup.1).sub.b I].sup.+ [HSO.sub.4 ].sup.-,

where R is a monovalent aromatic organic radical selected from the classconsisting of aromatic carbocyclic or heterocyclic having from 6-20carbon atoms, R¹ is a divalent aromatic organic radical, a is a wholenumber equal to 0 or 2, b is a whole number equal to 0 or 1, and the sumof a+b is equal to 1 or 2, or the valence of I, which comprises (A)effecting a coupling reaction between a C.sub.(6-30) aromatic compoundand potassium iodate in the presence of a mixture consisting essentiallyof acetic acid, acetic anhydride and sulfuric acid, and (B) recoveringthe resulting diaryliodonium bisulfate salt from the mixture of(A),wherein the improvement comprises substituting methylene chloridefor the acetic acid to produce an acetic acid-free mixture in thecoupling reaction, which is conducted at a temperature in the range offrom -25° C. to +25° C., whereby improved yields of diaryliodoniumbisulfate salt and shorter reaction times are achieved.
 2. A method inaccordance with claim 1, where the aromatic compound is benzene.
 3. Amethod in accordance with claim 1, where the aromatic compound istoluene.
 4. A method in accordance with claim 1, where the aromaticcompound is N-phenylmaleimide.
 5. A method in accordance with claim 1,where the aromatic compound is t-butylbenzene.
 6. A method in accordancewith claim 1, where the aromatic compound is o-xylene.